Chronic Lymphocytic Leukemia (CLL) is a disease of the white blood cells and is the most common form of leukemia in the Western Hemisphere. CLL represents a diverse group of diseases relating to the growth of malignant lymphocytes that grow slowly but have an extended life span. CLL is classified in various categories that include, for example, B-cell chronic lymphocytic leukemia (B-CLL) of classical and mixed types, B-cell and T-cell prolymphocytic leukemia, hairy cell leukemia, and large granular lymphocytic leukemia.
Of all the different types of CLL, B-CLL accounts for approximately 30 percent of all leukemias. Although it occurs more frequently in individuals over 50 years of age, it is increasingly seen in younger people. B-CLL is characterized by accumulation of B-lymphocytes that are morphologically normal but biologically immature, leading to a loss of function. Lymphocytes normally function to fight infection. In B-CLL, however, lymphocytes accumulate in the blood and bone marrow and cause swelling of the lymph nodes. The production of normal bone marrow and blood cells is reduced and patients often experience severe anemia as well as low platelet counts. This can pose the risk of life-threatening bleeding and the development of serious infections because of reduced numbers of white blood cells.
To further understand diseases such as leukemia it is important to have suitable cell lines that can be used as tools for research on their etiology, pathogenesis and biology. Examples of malignant human B-lymphoid cell lines include pre-B acute Iymphoblasticleukemia (Reh), diffuse large cell lymphoma (WSU-DLCL2), and Waldenstrom's macroglobulinemia (WSU-WM). Unfortunately, many of the existing cell lines do not represent the clinically most common types of leukemia and lymphoma.
The use of Epstein Barr Virus (EBV) infection in vitro has resulted in some CLL derived cell lines, in particular B-CLL cells lines, that are representative of the malignant cells. The phenotype of these cell lines is different than that of the in vivo tumors and instead the features of B-CLL lines tend to be similar to those of Lymphoblastoid cell lines. Attempts to immortalize B-CLL cells with the aid of EBV infection have had little success. The reasons for this are unclear but it is known that it is not due to a lack of EBV receptor expression, binding or uptake. Wells et al. found that B-CLL cells were arrested in the G1/S phase of the cell cycle and that transformation associated EBV DNA was not expressed. This suggests that the interaction of EBV with B-CLL cells is different from that with normal B cells. EBV-transformed CLL cell lines moreover appear to differentiate, possessing a morphology more similar to Iymphoblastoid cell lines (LCL) immortalized by EBV.
An EBV-negative CLL cell line, WSU-CLL, has been established previously (Mohammad et al., (1996) Leukemia 10(1): 130-7). However, no other such cell lines are known.
Various mechanisms play a role in the body's response to a disease state, including cancer and CLL. For example, CD4+T helper cells play a crucial role in an effective immune response against various malignancies by providing stimulatory factors to effector cells. Cytotoxic T cells are believed to be the most effective cells to eliminate cancer cells, and T helper cells prime cytotoxic T cells by secreting Th1 cytokines such as IL-2 and IFN-γ. In various malignancies, T helper cells have been shown to have an altered phenotype compared to cells found in healthy individuals. One of the prominent altered features is decreased Th1 cytokine production and a shift to the production of Th2 cytokines. (See, e.g., Kiani, et al., Haematologica 88:754-761 (2003); Maggio, et al., Ann Oncol 13 Suppl 1:52-56 (2002); Ito, et al., Cancer 85:2359-2367 (1999); Podhorecka, et al., Leuk Res 26:657-660 (2002); Tatsumi, et al., J Exp Med 196:619-628 (2002); Agarwal, et al., Immunol Invest 32:17-30 (2003); Smyth, et al., Ann Surg Oncol 10:455-462 (2003); Contasta, et al., Cancer Biother Radiopharm 18:549-557 (2003); Lauerova, et al., Neoplasma 49:159-166 (2002).) Reversing that cytokine shift to a Th1 profile has been demonstrated to augment anti-tumor effects of T cells. (See Winter, et al., Immunology 108:409-419 (2003); Inagawa, et al., Anticancer Res 18:3957-3964 (1998).)
Mechanisms underlying the capacity of tumor cells to drive the cytokine expression of T helper cells from Th1 to Th2 include the secretion of cytokines such as IL-10 or TGF-β as well as the expression of surface molecules interacting with cells of the immune system. OX-2/CD200, a molecule expressed on the surface of dendritic cells which possesses a high degree of homology to molecules of the immunoglobulin gene family, has been implicated in immune suppression (Gorczynski et al., Transplantation 65:1106-1114 (1998)) and evidence that OX-2/CD200-expressing cells can inhibit the stimulation of Th1 cytokine production has been provided. Gorczynski et al. demonstrated in a mouse model that infusion of OX-2/CD200 Fc suppresses the rejection of tumor cells in an animal model using leukaemic tumor cells (Clin Exp Immunol 126:220-229 (2001)).
Improved methods for treating individuals suffering from cancer or CLL are desirable, especially to the extent they can enhance the activity of T cells.